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Intracellular Axial Current in Chara corallina Reflects the Altered Kinetics of Ions in Cytoplasm under the Influence of Light

F. Baudenbacher ^*, L. E. Fong ^*, G. Thiel , M. Wacke , V. Jazbinsek , J. R. Holzer ^*, A. Stampfl  and Z. Trontelj 

^* Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235; Institute for Botany, Plant Biophysics, Darmstadt University of Technology, D-64287 Darmstadt, Germany; and Physics Department, Institute of Mathematics, Physics and Mechanics, University of Ljubljana, 1000 Ljubljana, Slovenia

Correspondence: Address reprint requests to Zvonko Trontelj, Physics Department, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia. Tel.: 386-1-476-6582; E-mail: zvonko.trontelj{at}fiz.uni-lj.si.

Recent experiments demonstrate that the concentration of Ca²⁺ in cytoplasm of Chara corallina internodal cells plays important role in electrical excitation of the plasma membrane. The concentration of free Ca²⁺ in the cytoplasm –[Ca²⁺]_c is also sensitive to visible light. Both phenomena were simultaneously studied by noninvasive measuring action potential (AP) and magnetic field with a superconducting quantum interference device magnetometer in very close vicinity of electrically excited internodal C. corallina cells. A temporal shift in the depolarization maximum, which progressively occurred after transferring cells from the dark into the light, can be explained by the extended Othmer model. Assuming that the change in membrane voltage during the depolarization part of AP is the direct consequence of an activation of [Ca²⁺]_c sensitive Cl^– channels, the model simulations compare well with the experimental data. We can say that we have an example of electrically elicited AP that is of biochemical nature. Electric and magnetic measurements are in good agreement.